Calciferous and similar deposits occur in body fluid passages of various types, including kidney stones, gall stones, and arterial plaque. Surgery or radiation typically has been used for removing or destroying such deposits. In one form of laser therapy, radiation is directed onto a light-receiving surface of a heat-generating element. The element is then placed in contact with the target deposit, melting it. This approach has several drawbacks which include, for example, thermal damage to surrounding tissue, formation of char and debris from advanced fibrous and calcified plaques, and adhesion of the hot element to the tissue thereby rupturing it when the element is removed.
In another approach, known as direct lasertripsy, laser radiation is applied directly to the target deposit to ablate it or produce shock waves that induce fragmentation. Direct lasertripsy also has several disadvantages. For example, laser energy often damages healthy tissue surrounding the target deposit by direct absorption or by acting as a general heat sink for the high temperature plasma. Some deposits only weakly absorb radiation which requires the use of higher levels of radiation and consequent tissue damage.
Impact lithotripsy has been used for treating some hard deposits. For example, Pohlman et al. in U.S. Pat. No. 3,927,675 describe a device for fragmenting hard deposits in the urinary tract using ultrasonic energy. This device has several drawbacks, including the use of a thick spiral metal probe within the catheter, and it requires that ultrasonic energy be transmitted the length of the catheter which causes vibration along the length of the catheter. In U.S. Pat. No. 3,823,717, Pohlman et al. describe another ultrasonic device having an implement with a cutting edge attached to the end of the catheter. This device suffers all the drawbacks of the other Pohlman device with the additional disadvantage that the cutting edge appears to be exposed, which could damage surrounding tissues.
Oinuma et al. in U.S. Pat. No. 4,605,003 describe a lithotripter which utilizes a gas-generating explosive to drive an impact element against a stone in a body. This device is capable of only a single pulse, which exhausts the explosive. Thus, if the impact misses the target or fails to break it, the catheter must be withdrawn, the explosive recharged and the catheter reinserted for each additional attempt.
Schmidt-Kloiber et al. in U.S. Pat. No. 3,785,382 describe a lithotripter which utilizes a driving mechanism based on a water-filled chamber in which a hydraulic wave is induced by electrodes and transmitted through a membrane to the lithotripter wire which is threaded into the body. The design of this device requires that the mechanical energy resulting from the hydraulic wave be transmitted over the length of the lithotripter wire, so that if the wire takes one or more turns in a convoluted body passage, much of the energy could be transmitted to healthy tissue before it reaches the stone.
It is an object of the present invention to provide a safe, effective catheter design which is free of these and other disadvantages.